Add Capsule3d module

[w0rm]

Capsule is a cylinder with hemispherical ends. This shape is useful in physics because of the ease of collisions.

The module could be very similar to the existing Cylinder3d, maybe except for the Capsule3d.from function, that could return something like Result Sphere3d Capsule3d in case of coincident points.

Extra functions to get a cylinder part of the capsule, or create a capsule out of cylinder could be useful too.